Linear motion guide units have been extensively installed in recent years between parts with slide relative to one another in machinery including machine tools, assembling machines, transporting machines, and so on. Of the different size and type linear motion guide units, there have been known sliders which have the carriages joined each other by couplers or connecting plates.
In a commonly-owned Japanese Utility Model Registration No. 2,565,426, there is disclosed a linear motion guide unit composed of a guide rail having raceway grooves extending lengthwise of the guide rail, a slider which fits over or conforms to the guide rail and has raceway grooves extending in opposition to the raceway grooves on the guide rail to define load-carrying races between them, and a plurality of rolling elements arranged in line in circulating circuits including the load-carrying races. The slider travels relatively to the guide rail via the rolling elements, which roll through the circuits while carrying heavy loads in the load-carrying races. The slider is further composed of plural carriages having the load-carrying races therein and juxtaposed in the lengthwise direction, and couplers having therein raceway grooves continuing the load-carrying races. The couplers are each interposed between two adjoining carriages. The raceway grooves in the couplers are somewhat larger in cross section than the load-carrying races in the carriage.
With the prior linear motion guide unit, the carriages are juxtaposed in the lengthwise direction and the couplers are made of synthetic resin and arranged between two adjacent carriages as stated earlier. The raceway grooves in the couplers, because they are larger than the load raceway grooves in the carriages, help relieve the rolling elements of a locally crowded or huddled state that would occur in the load-carrying races in the carriages. Moreover, retainer plates are secured to lower surfaces of the slider to join together the carriages in the lengthwise direction. The couplers are provided on their forward and aft ends thereof with projections raised above the ends and the carriages on their forward and aft ends thereof have recesses sunken below the forward and aft ends in complementary relationship to the projections on the ends of the adjoining couplers. Thus, the complementary relationship between the projections of the couplers and the recesses of the carriages help keep the carriages and the couplers from moving past each other in a direction perpendicular to the lengthwise direction of the slider. The retainer plates keep the rolling elements from falling away and apart from the raceway grooves in the carriages and have thereon lower seals. With the linear motion guide unit in which the carriages are joined to each other by the retainer plates fastened to the lower side of the slider, however, it is needed to reserve various types of the retainers in preparation for connections of carriages of different lengths. Moreover, the overall length of the slider is not increased by the lengthwise dimensions of the couplers. As the raceway grooves in the couplers have no construction taking part in carrying the loads applied to the slider, the increase in the load rating is less, compared with the increase in the length of the slider by the addition of the couplers.